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| United States Patent |
5,243,913
|
|
Brent
, et al.
|
September 14, 1993
|
Shock tube initiator
Abstract
A shock tube initiator comprises a plastics tubing having an unobstructed
axial bore, said tubing having throughout its length an inner surface upon
which unconsolidated reactive materials are provided as a loosely adherent
dusting of shock-dislodgeable particles at a core loading sufficiently low
to avoid rupture of the tubing in use, wherein said reactive materials
comprise flake metallic fuel particles having a surface colouring layer of
pigment, e.g. Fe.sub.2 O.sub.3 whereby on firing of the core charge the
residue is visibly of a different colour, hue, or shade.
| Inventors:
|
Brent; Geoffrey F. (Dundonald, GB6);
Harding; Malcolm D. (Irvine, GB6)
|
| Assignee:
|
Imperial Chemical Industries PLC (London, GB2)
|
| Appl. No.:
|
937605 |
| Filed:
|
September 2, 1993 |
Foreign Application Priority Data
| Current U.S. Class: |
102/275.8; 149/123 |
| Intern'l Class: |
C06C 005/00 |
| Field of Search: |
102/275.5,275.8
149/123
|
References Cited
U.S. Patent Documents
| 3590739 | Jul., 1971 | Persson | 102/275.
|
| 4222330 | Sep., 1980 | Krystyniak | 149/123.
|
| 4328753 | May., 1982 | Kristensen et al. | 102/275.
|
| 4363678 | Dec., 1982 | Nishimura et al. | 149/123.
|
| 4493261 | Jan., 1985 | Simon et al. | 102/275.
|
| 4537645 | Aug., 1985 | Yamaguchi et al. | 149/123.
|
| 4607573 | Aug., 1986 | Thureson et al. | 102/275.
|
| 4640035 | Feb., 1987 | Kind et al. | 102/275.
|
| 5166470 | Nov., 1992 | Stewart | 102/275.
|
Primary Examiner: Nelson; Peter A.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Claims
We claim:
1. A shock tube initiator comprising a plastics tubing having an
unobstructed axial bore, said tubing having throughout its length an inner
surface upon which a core charge of unconsolidated reactive materials are
provided as a loosely adherent dusting of shock-dislodgeable particles at
a core loading sufficiently low to avoid rupture of the tubing in use,
wherein said reactive materials comprise flake metallic fuel particles
having a surface colouring layer of pigment whereby on firing of the core
charge the residue is visibly of a different colour, hue, or shade.
2. The shock tube initiator claimed in claim 1 wherein the pigment is a
self-coloured metal oxide.
3. The shock tube initiator claimed in claim 2 wherein the metal oxide acts
as an oxidising agent at the temperatures typically attained by firing of
the shock tube.
4. The shock tube initiator claimed in claim 2 wherein the metal oxide is
vapour-deposited Fe.sub.2 O.sub.3.
5. The shock tube initiator claimed in claim 1 wherein the pigment makes up
less than 30% m/m based on the mass of the coloured metal flake.
6. The shock tube initiator claimed in claim 1 wherein the metal flake is
Al.
7. The shock tube initiator claimed in claim 6 wherein the reactive
materials comprise 10 parts (by weight) coated Al flake and 90 parts (by
weight) co-reagent.
8. The shock tube initiator claimed in claim 7 wherein the co-reagent
comprises a secondary explosive.
9. The shock tube initiator claimed in claim 8 wherein the secondary
explosive is HMX.
10. The shock tube initiator claimed in claim 7 wherein the co-reagent
comprises a powerful inorganic oxidising agent.
11. The shock tube initiator claimed in claim 10 wherein the inorganic
oxidising agent is Ba0.sub.2.
12. The shock tube initiator claimed in claim 1 wherein the core loading of
reactive materials is in the range of from less than about 20 mg/m to
about 100 mg/m.
Description
FIELD OF THE INVENTION
This invention concerns blasting operations in which shock-tube or
signal-tube transmission systems are used.
BACKGROUND OF THE INVENTION
Shock tubes and signal tubes are classes of low-energy fuse used in
blasting systems for transmitting an initiation signal from one point to
another (usually from one detonator or pyrotechnic delay to another), such
tubes being constructed of plastic, usually extruded and unreinforced, and
containing a particular detonating or rapid reacting pyrotechnic
composition distributed substantially uniformly along its central core at
relatively low loadings compared to common detonating cords. The
particulate composition is loosely adherent to the inner wall of the tube
so that it is shock-dislodgeable. The internal bore of the tubing is
usually narrow, and is normally circular (though it need not be). Shock
tube, for example, will typically consist of extruded plastic tube of
internal diameter around 1 mm with a core loading of, say, HMX/AL (94:6
parts by weight) of below 20 mg/m. Signal tube designed for lower signal
transmission speeds (i.e. significantly below 2 km/s) will have similar
dimensions, and will contain a rapid reacting pyrotechnic composition
comprising a metal fuel e.g. Al or quasi-metal fuel such as Si and a
powerful inorganic oxidising agent (especially BaO.sub.2) typically at a
core loading of around 20 mg/m to 100 mg/m. Reference may be made to
European Patent No. 327 219 (ICI) for further information on shock tube
products.
In field or mine situations it is not always immediately apparent to a
blast engineer that a particular tube has fired merely from visual
inspection of the still intact tube. This is in part because the visible
colour change of the core material upon detonation or reaction may not be
significant, especially at low core loadings. A further reason is that
accessories producers prefer to supply coloured products and so the
plastic of the shock/signal tube usually will be self-coloured, thus
masking to a significant degree any core colour change that might
otherwise have been perceptible. Additionally, natural or artificial light
levels, especially underground, are not always at an intensity or spectral
breadth conducive to perceiving a colour change in core material.
The Applicants have experimented with adding reactive pigment particles to
the shock/signal tube core charge. The results were generally poor
because, for a noticeable colour change, levels of pigment had to be used
which caused fundamental disturbance of the firing performance of the
tube. The present invention has overcome this problem, allowing
achievement of marked colour change while using only a relatively small
amount of reactive pigment.
SUMMARY OF THE INVENTION
According to the present invention, a shock/signal tube has a core charge
containing flake metallic fuel and the surface of the flake is coloured by
a layer of pigment so that on firing of the core charge the metallic fuel
is consumed, the pigment is dispersed, consumed or destroyed, and the
residue is visibly of a different colour, hue, or shade.
The core charge may be of the metal fuel/secondary explosives type, e.g.
Al/HMX, or the metal fuel/oxidiser type, e.g. Al/BaO.sub.2.
The pigment is most suitably a self-coloured metal oxide, preferably one
that is an oxidising agent at high temperatures. Especially suitable is
vapour-deposited Fe.sub.2 O.sub.3 ; it is effective at low deposition
levels and does not adversely interfere with the principal
performance-determining tube reactions.
In general the pigment will make up less than 30% m/m based on the mass of
the coloured metal flake, and will coat both sides of the flake.
Obviously, any bulk colouring of the plastics tube would have to be matched
to the colour change of the core charge so that the colour change is not
masked.
A further benefit which may result from metal flake coating with pigment is
that the flakes may be rendered non conducting, a welcome safety advantage
.
DESCRIPTION OF THE DRAWING
In the single figure attached a section through a shock or signal tube
initiator is shown wherein tubing 1 has throughout its length an inner
surface upon which unconsolidated reactive materials 2 are provided as a
loosely adherent dusting of shock-dislodgeable particles.
EXAMPLES
Two core charges were made up using coloured Al flake as the metal fuel and
HMX and BaO.sub.2, respectively, as the co-reagent. The Al flake was
coated with vapour-deposited Fe.sub.2 O.sub.3 sufficient to give the flake
a distinct gold colour. The ratio of coated Al to co-reagent was 10:90 by
weight. The c.Al/HMX mixture fired at 2050 m/s and the c.Al/BaO.sub.2
mixture fired at 650 m/s at loadings of 20 mg/m and 30 mg/m respectively
in clear `Surlyn` tubing (1.3 mm I.D.). Before firing the coloured core
charge was visible; after firing the tube looked clear.
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